Area Forecast Discussion
Issued by NWS Chicago, IL

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000
FXUS63 KLOT 151620
AFDLOT

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE CHICAGO/ROMEOVILLE IL
1120 AM CDT MON SEP 15 2014

.DISCUSSION...
311 AM CDT

DISMAL AND SHOWERY WEATHER ON TAP TODAY FOLLOWED BY PRETTY
SPECTACULAR WEATHER THE REMAINDER OF THE WEEK.

FAIRLY ENERGETIC SHORTWAVE TROUGH OVER THE DAKOTAS THIS MORNING
WILL DIG SOUTHEASTWARD INTO THE LOWER LAKES LATER TODAY BEFORE
SHIFTING EAST OF THE REGION TONIGHT. LOW-MID LEVEL FRONTOGENESIS IN
THE RIGHT ENTRANCE REGION OF 100KT+ 250MB JET IS ALREADY SUPPORTING
A BAND OF RAIN FROM EASTERN SD EAST INTO CENTRAL WISCONSIN. IN
ADDITION...SECOND AREA OF SHOWERS AND THUNDERSTORMS DEVELOPING OVER
IOWA IN ASSOCIATED WITH STRENGTHENING LOW LEVEL JET/WAA. THESE TWO
REGIONS OF PRECIP ARE LIKELY TO CONGEAL AND SPREAD ACROSS OUR CWA
LATER THIS MORNING AND CONTINUE INTO THE AFTERNOON. SOME WEAK
ELEVATED INSTABILITY COULD SUPPORT AN ISOLATED THUNDERSTORM SOUTH
BUT CHANCES AND AREAL COVERAGE OF THUNDER APPEAR LOW. AS TROUGH AXIS
TRANSLATE QUICKLY EASTWARD LOOK FOR RAIN/SHOWERS TO END...POSSIBLY
AS A PERIOD OF DRIZZLE LATER THIS AFTERNOON. TEMPS ARE TRICKY AND
WILL HINGE ON HOW MUCH THEY CAN RISE BEFORE RAIN STARTS AND THEY
LOSE A LITTLE GROUND THIS AFTERNOON.

STRONG SUBSIDENCE AND DRYING ARE FORECAST IN THE WAKE OF THE TROUGH
WHICH SHOULD LEAD TO RAPID CLEARING THIS EVENING WITH ANOTHER FAIRLY
HEALTHY PUSH OF EARLY SEASON COLD AIR ARRIVING TONIGHT. ONCE AGAIN
LOOKING FOR LOWS TO DROP INTO THE 30S OVER WESTERN PORTIONS OF THE
CWA...PARTICULARLY THE TYPICALLY FAVORED COOL SPOTS. CANT RULE OUT A
TOUCH OF FROST IN THE SHELTERED COOL SPOTS...ESPECIALLY ON ELEVATED
OBJECTS...BUT NOT EXPECTED TO BE A BIG ENOUGH DEAL TO INCLUDE IN
GRIDS.

TUESDAY LOOKS TO BE SUNNY AND UNSEASONABLY COOL...BUT NOT AS CHILLY
AS LAST WEEK. A SLOW BUT STEADY WARMING TREND WILL COMMENCE
WEDNESDAY AND CONTINUE INTO THE WEEKEND WITH HIGHS EVENTUALLY
REBOUNDING BACK TOWARD IF NOT A BIT ABOVE AVERAGE TOWARD THE
WEEKEND. NO RAIN IS EXPECTED THROUGH FRIDAY WITH PLENTY OF SUNSHINE
AND ALL AROUND PLEASANT WEATHER. MEDIUM RANGE MODELS DO SUGGEST
PATTERN COULD TURN POTENTIALLY STORMIER NEXT WEEKEND AS FLOW
FLATTENS OUT A BIT AND WARM AIR ADVECTION STRENGTHENS IN ADVANCE OF
TROUGH DIGGING INTO THE NORTHERN/CENTRAL PLAINS. STILL SOME
DISAGREEMENT IN THE DETAILS...NOT SURPRISINGLY THIS FAR OUT...SO
KEPT POPS MODEST FOR NOW UNTIL DETAILS CAN BE BETTER PINNED DOWN IN
THE COMING DAYS.

IZZI

&&

.AVIATION...

//ORD AND MDW CONCERNS...UPDATED 16Z...

* WIND DIRECTION AND SPEEDS ASSOCIATED WITH FROPA THIS AFTERNOON
  ...NORTH-NORTHEAST WIND LOOKING LIKELY BY LATE AFTERNOON...WIND
  SPEEDS COULD REMAIN UNDER 10 KT.
* CIGS LOWERING TO MVFR WITH SHRA.

BMD/KB

//DISCUSSION...UPDATED 12Z...

A COLD FRONT STRETCHES ACROSS CENTRAL LAKE MICHIGAN INTO CENTRAL
IOWA EARLY THIS MORNING AND WILL SLOWLY SAG TOWARDS THE REGION
THROUGH THE DAY. OUT AHEAD...A FEW EARLY MORNING HIGH BASED SHOWERS
AND THUNDERSTORMS HAVE DEVELOPED ASSOCIATED WITH A MID LEVEL SPEED
MAX. MOST INTENSE ACTIVITY THUS FAR HAS MOSTLY BEEN FOCUSED SOUTH OF
THE TERMINALS THIS MORNING BUT THE AREA OF SHRA/TSRA MOVING INTO
NORTHWEST IL WILL ARRIVE AT THE TERMINALS OVER THE NEXT FEW HOURS.
THERE IS SOME VERY MODEST INSTABILITY WITH EQUILIBRIUM LEVELS DEEP
ENOUGH TO SUPPORT AT LEAST AN ISOLATED LIGHTNING THREAT BUT FOR NOW
LOW COVERAGE WOULD PRECLUDE MENTION OF TS IN TAF AND WILL MAINTAIN
SHRA. AS THE COLD FRONT SAGS SOUTH ACROSS THE TERMINALS LATER
TODAY...GUIDANCE HAS COME INTO BETTER AGREEMENT THAT THERE WILL BE A
WIND SHIFT TO THE N...POSSIBLY NNE...BEFORE WINDS SETTLE BACK TO A
NW DIRECTION LATER TODAY. THERE MAY BE A BRIEF UPTICK IN THE WINDS
MID AFTERNOON INTO THE 10-12KT RANGE. CIGS WILL ALSO DECREASE AS THE
FRONTAL TROUGH APPROACHES WITH THE POTENTIAL FOR SEVERAL HOURS OF
MVFR CIGS THIS AFTERNOON AND EARLY EVENING. DRIER AIR MOVING IN THIS
EVENING SHOULD ALLOW CIGS TO SCATTER OUT FOR TONIGHT WITH A RETURN
TO VFR CONDITIONS. WINDS ARE EXPECTED TO DIMINISH OVERNIGHT AND
DEPENDING ON HOW QUICKLY SKIES CLEAR WILL HAVE TO KEEP AN EYE ON THE
FOG POTENTIAL...ESPECIALLY AT RFD WITH FUTURE TAF UPDATES.

BMD

//ORD AND MDW CONFIDENCE...UPDATED 16Z...

* MEDIUM TO HIGH CONFIDENCE IN WIND DIRECTION...LOW-MEDIUM THAT WINDS
  WILL GET AS HIGH AS 10 KT LATE THIS AFTERNOON.
* LOW-MEDIUM CONFIDENCE IN SHRA/MVFR TIMING.

BMD/KB

//OUTLOOK FOR ORD/MDW FOR 00Z WEDNESDAY-12Z MONDAY...UPDATED 12Z...

TUESDAY NIGHT THROUGH FRIDAY...PRIMARILY VFR.
SATURDAY THROUGH SUNDAY...PERIODIC CHANCES FOR THUNDERSTORMS.

BMD

&&

.MARINE...
303 AM CDT

LOW PRESSURE NEAR JAMES BAY THIS MORNING WILL DRAG A COLD FRONT
ACROSS LAKE MICHIGAN. WINDS WILL TURN NORTHWEST TO NORTH BEHIND THE
FRONT...AND MAY BRIEFLY INCREASE INTO THE 20 TO 25 KT RANGE
ESPECIALLY ON THE SOUTH END OF THE LAKE THIS EVENING. HIGH PRESSURE
WILL BUILD IN BEHIND THE FRONT ALLOWING WINDS TO REMAIN MODEST FOR A
PERIOD BEFORE SOUTHWEST FLOW BEGINS TO FRESHEN UP AGAIN OVER THE
NORTH HALF OF LAKE MICHIGAN MIDDAY TUESDAY. ANOTHER COLD FRONT WILL
DIVE SOUTH ACROSS LAKE MICHIGAN ON WEDNESDAY TURNING WINDS NORTH TO
NORTHEAST AND INCREASING FOR A SHORT PERIOD TO AROUND 30 KT ONCE
AGAIN.

BMD

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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